In recent years, there has been an increasing number of energy systems which simultaneously handle various energy forms, from the standpoint of global environmental protection and energy conservation.
For example, a so-called cogeneration system, in which waste heat is recovered from electric power facilities at the time of electric power generation and is converted into heat conforming to the form of utilization and supplied together with electric power, aims to achieve extremely high total efficiency, nearly double the efficiency when only the generated electric power is used.
FIG. 7 is a graph showing the change with time in electric power demand and heat demand in one day in a certain region; the horizontal axis represents time, and the vertical axis represents the electric power load and heat load. As is clear from FIG. 7, in general heat is supplied simultaneously with electric power, and so in essence the coincidence, in terms of both quantity and time, of electric power demand state and the heat demand state is a condition to achieve high total efficiency in a cogeneration system.
However, in actuality the electric power demand state and the heat demand state do not necessarily coincide, and so when supply of either electric power or of heat is matched to demand, the problem occurs that the total efficiency which initially had been expected is not obtained. Hence a measure is conceivable in which, by introducing an electricity storage equipment or a heat storage equipment, high total efficiency is secured.
In a system in which an electricity storage equipment or a heat storage equipment, or both, is introduced, when considering operation during a certain term, questions include the timing with which power charge or heat charge by a electricity storage equipment or heat storage equipment is rational, or the timing with which power discharge or heat discharge from an electricity storage equipment or heat storage equipment is rational. When considering operation of an electricity storage equipment or heat storage equipment during a certain term, due to constraints on the capacity of the electricity storage equipment or heat storage equipment, unconditional continuation of power discharge or of heat discharge is not possible, and the need arises to perform power charge or heat charge in a certain time period equal to the amount of reduction in charged power or charged heat due to power discharge or heat discharge in a different time period, to restore the amount of power charge or heat charge. Further, it is expected that, instead of considering these equipments independently, simultaneous optimization will be more effective.
In methods of energy system operation scheduling of the prior art, for example in relation to electricity storage equipments, generally time periods for power charge at nighttime and time periods for power discharge during electric power load peaks are decided, and schedules for operation are created according to rules.
Among such energy system operation scheduling methods, there are some which suggest that mixed-integer programming problems can be directly applied (Patent Document 1). Further, as an alternative, a method has been proposed in which a metaheuristic method is applied and an approximate solution is found (Patent Document 2).    Patent Document 1: Japanese Patent Laid-open No. 2005-257097    Patent Document 2: Japanese Patent Laid-open No. 2004-171548    Non-patent Document 1: Iwanami Kouza: Ouyou Suugaku 15 (Houhou 7), Saitekika Hou (Hiroshi Fujita, Hiroshi Konno, Kunio Tanabe (1998))
Among energy system operation scheduling methods of the prior art for an energy system which simultaneously handles various forms of energy, a practical method for determining an operation schedule which simultaneously optimizes two or more types of energy storage equipments has not been established, and so it could not be said that operation was necessarily optimized, viewing the energy system as a whole.
For example, when applying a mixed-integer programming problem disclosed in Patent Document 1, problems that can be handled using current technology are limited to mixed-integer quadratic programming problems, so that the fuel consumption characteristics of equipment existing in the energy system are limited to simple characteristics represented by downward convex quadratic equations. Further, in general such mixed-integer quadratic programming problems are often not for practical purposes soluble, due to constraints on computation time.
Further, when applying a metaheuristic method disclosed in Patent Document 2, although in general a solution is obtained using a metaheuristic method in a practical amount of computation time, often ease of explanation is lacking, and there has been the problem that solution analysis is difficult.